In general, the surface of a metallic article may be alloyed by the simultaneous and cooperative operation of a laser beam and an alloy powder. To accomplish this, systems have been proposed incorporating a laser source and focusing apparatus, with a powder delivery apparatus provided as part of an integral package. The laser beam melts a relatively small area at the surface of the article, and a controlled volume of alloying particles are delivered into the melt pool.
As an example, gas turbine engines, such as utilized with jet aircraft, are being designed with ever increasing performance requirements. One element of the engine which has been receiving attention is the seal created between the rapidly rotating blades and the surrounding casing. The combustion gases exiting the engine through the rotating blade system should be properly channeled and not be permitted to otherwise escape if efficiencies are to be maximized. It has been the practice to provide the blade tips with abrasive particles which scour the surface of an abradable material mounted in the surrounding casing in order to create a seal which prevents escape of the gases. The blades not only elongate during operation of the engine on account of temperature changes, but also move transverse to their axis of rotation as a result of aircraft operating conditions. Permitting the blade tips to scour the abradable material mounted in the casing allows a very tight dynamic seal to be formed.
Particulates have been applied to blade tips by various means, generally involving some sort of electrodeposition or sintering process. Neither of these processes, however, creates a fusion bond between the particulate and the blade tip. The particulates may become loosened from the tip during operation of the engine, with the result that engine efficiency may diminish over time.
The present invention is directed to a nozzle for applying particulates to a turbine engine blade tip through the use of a particulate delivery nozzle in conjunction with a laser beam. The nozzle causes the supplied particulates to exit coaxially with a selected shield gas, and an internal diffusion system assures that the shield gas is not channelized when exiting the nozzle.